GB2174220A - Autocorrelator - Google Patents

Abstract

A multidimensional autocorrelator, eg a parallel three dimensional digital autocorrelator for a pseudo-random binary sequence (PRBS), has a digital memory 20, one scanner 21 to read delay zero plus three scanners 22,23,24 to read each delay dimension, modulo two adders 25,26 effectively operating as multipliers with totalizers 27 to find correlation values of more than one delay point in parallel, a counter 29 to set the correlation cycle and a limit comparator 28 to compare the values of correlation with set limits corresponding to exact agreement or opposition over one correlation cycle, which if reached then a signal is activated indicating the existance of an 'anomaly' possibly suitable to be used to predict the behaviour of the available PRBS data. The delays may be adjusted. Analogue devices may be used (Fig. 1). <IMAGE>

Description

SPECIFICATION A multidimensional autocorrelator This invention relates to an electronic circuit to seek the prediction of the behaviour of pseudo random binary signals from relatively small amount of data.

Autocorrelation is a well known signal processing technique, it is usually used to study the relationship between a signal and its exact image displaced in time with a certain delay.

Multidimensional autocorrelation is a technique to study the relationship between a signal and its exact images, all of which are displaced in time with certain delays.

Pseudo Random Binary Signals (PRBS) are well known signals, they are usually used to test dynamic systems and to encode data.

PRBS are formed of repetitive cycles and are usually generated from shift registers with relatively much shorter lengths compared with PRBS cycle lengths.

When using PRBS as a stimulus in correlation techniques, it is usual to correlate or integrate over entire cycle lengths.

It can be useful in some applications, such as nonlinear systems testing and decoding, to predict the behaviour of PRBS from a part of one cycle length, rather than from complete cycle lengths.

The present invention provides for a multidimensional autocorrelator whose main function is to seek the location of a type of what is known as anomalies or deterministic characteristics present in multidimensional autocorrelation functions of PRBS.

The location of anomalies found by the subject invention provides the ability to predict with reasonable accuracy the behaviour of PRBS subject to the following two assumptions: 1. The data available is an unbroken and error free part of one PRBS cycle and is more than one shift register length. 2. Correlation cycle is more than one shift register length.

According to the present invention there is provided a multidimensional autocorrelator comprising a memory to store some or all of the available data, scanners to read data from the memory thereof corresponding to delays zero and one delay for each dimension, multiplier(s) followed by integrator(s) or their digital equivalants to find autocorrelation values, limit comparator(s) to compare autocorrelation values to set limits and to give signal when any limit is reached and a correlation cycle counter to give start and stop signals. The presence of power supplies, clock circuits and circuits normaly necessary to the operation of similar circuits is implicit.

Two specific embodiments of the invention will be described by way of examples with reference to the accompanying block diagram drawings in which: Figure 1 is the block diagram of the first example being a serial two dimensional analogue autocorrelator.

Figure 2 is the block diagram of the second example being a parallel three dimensional digital autocorrelator.

Referring to Fig. 1 the serial two dimensional analogue autocorrelator comprises a memory 10, reading from the memory 10 are three scanners, the first scanner 11 reads data corresponding to delay zero, the second scanner 12 reads data corresponding to the first dimension delay and the third scanner 13 reads data corresponding to the second dimension delay.

The outputs from all three scanners are fed to the multiplier(s) 14 which may be realized using methods familiar to suitably knowledgeable persons, such methods include but are not limited to the use of the following components; Analogue multipliers, logarithmic amplifiers, adders, modulators and correlators.

The output from the multiplier(s) 14 is fed to the integrator 15 which has memory for one value of data. The integrator 15 may be realized using the following or similar components; Operational amplifiers, inductance in series with resistance and correlators. The start and stop signals to the integrator 15 are generated by the counter 17 at the beginning and end of the integration cycle respectively.

The counter 17 may be realized by using a digital counter or similar circuit.

An additional stop signal may be provided by a circuit (not shown) which activates before the end of an integration cycle when any bit out of the multiplier(s) 14 is in opposite correlation to any preceeding bit within the integration cycle.

The limit comparator 16 may be realized using Schmitt triggers or similar circuits.

The comparator 16 receives triggering from the counter 17 stop signal, if threshold is reached then output signal from the comparator 16 is used as a trigger signal to indicate the existance of an anomaly.

Stop signals may be used to automatically advance delay(s) to values not used in previous measurements through programming an additional circuit (not shown).

In order to operate the subject autocorrelator to seek an anomaly, the available PRBS data is read in whole or in part into the memory 10 and the integration cycle is set into the counter 17 to not less than the expected shift register length.

The limit comparator 16 is set either automatically or manually to correspond to exact agreement or exact opposition between the multiplied delayed PRBS and the zero delay PRBS data.

At this stage, autocorrelation may begin starting with any values of delays and proceeding by, for example, fixing one delay value while advancing the other one bit at a time correlating to a preprogrammed limit, after the correlation of which the first delay is advanced one bit and the second delay is returned to the next to the first delay.

When an anomaly is found, the limit comparator 16 would give a trigger signal, which may be used to either stop the search or to continue after registering the corresponding delays, the trigger signal may also start prediction of PRBS using delays corresponding.to anomaly found.

Referring to Fig. 2, the parallel three dimensional digital autocorrelator comprises a digital memory 20. Reading from the memory 20 are four scanners, the first 21 reads the foremost data bit corresponding to delay zero. The second 22, third 23 and fourth 24 scanners read data bits corresponding to first, second and third dimension delays respectively. The output from the second 22, third 23 and fourth 24 scanners are fed to a modulo two adder 25 being a digital equivalant of analogue multiplier for PRBS input. The output from the afore-mentioned adder 25 plus the output from the first scanner 21 are fed to another modulo two adder 26 whose output is fed to the totalizer 27.The totalizer 27 has more than one location to accumulate autocorrelation values in parallel, the electronics for distributing consecutive readings in correspondingly different memory locations in the totalizer 27 is implicit. The start and stop signals, either of which may be used to return to zero, can be generated by the correlation cycle counter 29.

Autocorrelation values from the memory locations of the totalizer 27 are fed in parallel, or scanned, to the limit comparator 28. If no exact agreement or opposition is achieved over a complete correlation cycle or less then the comparator 28 activates a stop signal. If exact agreement or opposition is achieved over one complete correlation cycle then the comparator 28 activates a signal to indicate the existance of one or more anomalies. Stop signal can be used to automatically advance delays to values not used in previous measurements by an additional circuit (not shown).

The realization of the subject autocorrelator may be made using components such as discreet logic or microprocessors or the autocorrelator may be built in whole or in part on on an integrated circuit.

In order to operate the subject autocorrelator to seek an anomaly, the available data is read in whole or in part to the memory 20, then the correlation cycle length is set to the counter 27 to a limit not less than the maximum expected shift register length. The limit comparator 28 is set either manually or automatically to limits corresponding to exact agreement or exact opposition of correlation over one correlation cycle.

On starting to correlate, the values of autocorrelation for each of the totalizer 27 memories are updated from an initial value of zero.

If any value of autocorrelation reaches the set limit of the comparator after one correlation cycle then a signal is activated, which can be used to, for example, record the corresponding delays or stop correlation or to start predicting new PRBS based on the found anomaly.

If no value of correlation reaches the set limit, then new delay values are entered to the scanner and the correlation cycle is repeated.

Claims (6)

1. A multidimensional autocorrelator comprising a memory to store some or all of the available PRBS data, scanners to read data from the memory thereof corresponding to delays zero and one delay for each dimension, multiplier(s) followed by integrator(s) or their digital equivalant to find autocorrelation values, limit comparator(s) to compare autocorrelation values to set limits and to give signal when any limit is reached and a correlation cycle counter to give start and stop signals. The presence of power supplies, clock circuits and all circuits normally necessary for the operation of similar circuits is implicit.

2. A multidimensional autocorrelator as claimed in claim 1 wherein an additional circuit is included to monitor the values of autocorrelation and the counter simultaneously in order to activate a stop signal when non of the autocorrelation values are in exact agreement or exact opposition over less than one correlation cycle.

3. A multidimensional autocorrelator as claimed in claim 1 or claim 2 wherein two clock speeds are used simultaneously, one speed is faster than the other by a multiplication factor of not less than one correlation cycle.

4. A multidimensional autocorrelator as claimed in claim 1 or claim 2 or claim 3 wherein any one or combination of components are realized in whole or in part by integrated circuits with similar functions.

5. A multidimensional autocorrelator as claimed in claim 4 forming a part of a larger system.

6. A multidimensional autocorrelator substantially as described herein with reference to Fig. 1 and to Fig. 2 of the accompanying block diagram drawings.